1. Field of the Invention
This invention relates to a planographic printing plate material (i.e., a lithographic printing plate), more particularly, to a non-treatment type planographic printing plate material which can be mounted on a printing machine and printed without applying any treatment after exposure.
2. Description of the Prior Art
In this specification, a material for producing a planographic printing plate i.e., the material before exposure to light, and a planographic printing plate produced from the material are called a "planographic printing plate material" and a "planographic printing plate", respectively.
Hitherto, as planographic printing plates those plates called a deep-etch plate and a pre-sensitized (PS) plate have been most widely used.
A deep-etch plate is produced by the steps of coating a negative type light-sensitive resin on a sand grained aluminum or zinc plate, developing after printing a positive original thereon, rubbing in a tincture after or without etching, providing a lacquer thereon, and then peeling off the hardened light-sensitive resin layer.
On the other hand, PS plates mainly have a structure where a light-sensitive resin is coated on an aluminum plate. In the case of such a PS plate, an image is printed using a positive original (mask) or negative original (mask) and developed, and then a developing ink or protective lacquer is provided on the hardened light-sensitive resin layer constituting the image areas, whereby the printing plate is obtained. In this way, while the treatment steps required for the production of a PS plate are greatly simplified as compared with the deep-etch plate, steps such as development, etc., are still needed.
Recently, planographic printing plate materials in which treatment after exposure is omitted and which can be mounted on a printing machine and printed immediately after exposure without applying any chemical treatments have been proposed. In this specification, such a printing plate material is called a "non-treatment type" printing plate material in the sense that no treatment is applied as described above. The details of such a non-treatment type printing plate material are described in U.S. Pat. No. 3,707,372.
This non-treatment type planographic printing plate is produced from a radiation-sensitive member having a three layer structure in which a metallic first layer, a second layer of a material capable of forming a reaction product on reacting with the above first layer upon exposure to electromagnetic radiation, and a third layer of material unreactive with the above second layer are bonded to each other. In this case, an electromagnetic radiation image is projected onto the above second layer through the first or third layer, thus selectively forming the above reaction product, and thus the relationship of their hydrophilic nature to their oleophilic nature of the areas where the above reaction product is formed is different from that of the unreacted areas, whereby a planographic printing plate is obtained.
However, conventional non-treatment type planographic printing plate materials such as the above have an insufficient shelf life since an undesirable interaction between the first layer and the second layer of the material often occurs during storage. Moreover, since such conventional non-treatment type planographic printing plate materials after exposure have an insufficient difference in the relationship of their hydrophilic nature to their oleophilic nature, such materials cannot be employed as a printing plate for practical use.